# Fat Titanium Tandem



## Lars_D (May 24, 2011)

Here is an initial drawing of a project I am working on. I'd be interested in any suggestions from the forum. My wife and I are both fairly tall (I'm 6'2 she's 5'8); my thinking is that with minor adjustments (e.g. stems and handlebars) we'd both fit in either position.


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## Erichimedes (Jul 30, 2010)

Is the image hosted anywhere I could see it in more detail? I'd be curious to look at your numbers a little closer. What is your stoker effective top tube length? I built our tandem MTB last fall, and I sort of love the tandem framebuilding niche. I see no reason you and your wife couldn't swap. How long is the captain seat tube? When we try to switch, my stoker's fine until we try to stand over the bike.

Are you building this yourself, or having a framebuilder do it?


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## Lars_D (May 24, 2011)

Erichimedes said:


> Is the image hosted anywhere I could see it in more detail? I'd be curious to look at your numbers a little closer. What is your stoker effective top tube length? I built our tandem MTB last fall, and I sort of love the tandem framebuilding niche. I see no reason you and your wife couldn't swap. How long is the captain seat tube? When we try to switch, my stoker's fine until we try to stand over the bike.
> 
> Are you building this yourself, or having a framebuilder do it?


If you select the image you should be able to get a better look. A builder is building the frame. I'll select and assemble the parts. The stand over in front is about 31.5 inches--it should be okay for my wife.


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## Erichimedes (Jul 30, 2010)

Nice, this will probably be a really fun bike. I've selected the image and then zoomed in on the result, and cannot quite read the numbers. Really, if you have a builder involved, I wouldn't want to comment on his work too much. If you've selected him to build your bike, trust what he says. The one thing I'll say, and take it with a grain of salt, but it's very easy to build a tandem with too short of a stoker's effective top tube length (same as distance between bottom brackets). Ours is 740mm, and our team is smaller than yours. I would choose somewhere close to 770mm in your case. Trying to save 30mm of wheelbase here is pointless and can make both of you less comfortable. You're riding something with a 7 foot wheelbase, trying to shorten it by an inch is silly.

All this being said, yours could be that long or longer, I just can't read the drawing.


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## Lars_D (May 24, 2011)

Erichimedes said:


> Nice, this will probably be a really fun bike. I've selected the image and then zoomed in on the result, and cannot quite read the numbers. Really, if you have a builder involved, I wouldn't want to comment on his work too much. If you've selected him to build your bike, trust what he says. The one thing I'll say, and take it with a grain of salt, but it's very easy to build a tandem with too short of a stoker's effective top tube length (same as distance between bottom brackets). Ours is 740mm, and our team is smaller than yours. I would choose somewhere close to 770mm in your case. Trying to save 30mm of wheelbase here is pointless and can make both of you less comfortable. You're riding something with a 7 foot wheelbase, trying to shorten it by an inch is silly.
> 
> All this being said, yours could be that long or longer, I just can't read the drawing.


Good point. The stoker stem and seat will reduce the reach by about 20cm, so yes, the 73.6 cm reach for mine seems pretty short. Here is the current picture.
View attachment Tandem v2.pdf
I had the builder add a rear rack and narrow the rear end slightly. I'll also suggest the longer effective stoker top tube.


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## PMK (Oct 12, 2004)

Before posting any real comments, how serious is the bike intended use in regards to technical riding.

When I designed the tandem I wanted built, but never pulled the trigger on doing it, I considered everything I thought as a drawback and tried to overcome it. The primary concerns were chainrings clearance and protection, keeping the timing chain better protected when going over stuff, adding ground clearance without adding height or much weight, building in the mounts for a glide plate and frame protection and finally designing as part of the structure, onboard storage compartments for common items like a pump, tire repair items and tools. 

Maybe someday.

PK


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## Lars_D (May 24, 2011)

PMK said:


> Before posting any real comments, how serious is the bike intended use in regards to technical riding.
> 
> When I designed the tandem I wanted built, but never pulled the trigger on doing it, I considered everything I thought as a drawback and tried to overcome it. The primary concerns were chainrings clearance and protection, keeping the timing chain better protected when going over stuff, adding ground clearance without adding height or much weight, building in the mounts for a glide plate and frame protection and finally designing as part of the structure, onboard storage compartments for common items like a pump, tire repair items and tools.
> 
> ...


I don't think we will be doing technical riding. We'll ride it on the multi-use trails in Anchorage (which are not technical) and, during the winter, the frozen rivers North of town (the Susitna, Yentna, and Skwentna rivers). Storage will be in frame bags and rack-mounted panniers .


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## Sanchofula (Dec 30, 2007)

If it's for multi use trails, non technical terrain, I'd suggest you skip the front suspension and instead size the fork and rear triangle for plus sized tires, specifically 29+. This is how we've been running our El Jefe for moderate trails and it works well. The only reason I am running a suspension fork is because we do highly technical terrain.

For sure you want thru axles for frame and wheel stability.

Titanium is very flexy and the only way to make it as stiff as steel or aluminum is to overbuild it, which then increases the weight to the point that the titanium has no advantage over other metals other than being more expensive.

Get a Rohloff geared hub, skip the derailleurs.

Consider a bent top tube for your stoker, it makes mounting easier for short people; also helps with emergency dismounts.

If you want the most comfortable tandem possible; I'm only saying this because money is generally no object when someone is looking at a ti custom frame, I'd get it built as a full suspension plus whcih woudl make your stoker very happy


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## Lars_D (May 24, 2011)

Nurse Ben said:


> If it's for multi use trails, I'd suggest you skip the front suspension and instead size the fork and rear triangle for plus sized tires, specifically 29+.
> 
> For sure you want thru axles for frame and wheel stability.
> 
> ...


Thanks, Ben. I am not a fan of suspension systems--too complex and heavy. The builder shows a front suspension in the drawing, but I plan on using a rigid front fork from a Surly Ice Cream Truck which fits 4.8 inch tires. The back will also accommodate that size tire and there will also be a thud buster seatpost for the stoker (me). Because of the winter river rides, I'll likely use Dillinger 5 tires on 90 or 100mm wide rims (Black Floyd tires will be for the summer). For transmission I'll have no front shifters and a simple 9-speed 11-32 cassette in the rear. The timing chain will be on the right side, inboard of the drive chain with a 32t drop stop chain wheel.


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## Sanchofula (Dec 30, 2007)

Lars_D said:


> Thanks, Ben. I am not a fan of suspension systems--too complex and heavy. The builder shows a front suspension in the drawing, but I plan on using a rigid front fork from a Surly Ice Cream Truck which fits 4.8 inch tires. The back will also accommodate that size tire and there will also be a thud buster seatpost for the stoker (me). Because of the winter river rides, I'll likely use Dillinger 5 tires on 90 or 100mm wide rims (Black Floyd tires will be for the summer). For transmission I'll have no front shifters and a simple 9-speed 11-32 cassette in the rear. The timing chain will be on the right side, inboard of the drive chain with a 32t drop stop chain wheel.


Oh, gotcha, this is a fat bike!

I also use an ICT, same drivetrain set up as you but 10sp; I assume you're doing 9sp to keep things skinny and not have tire to chain contact.

Check out the 29+ option for summer riding, we have Surly Dirt Wizards, very nice ride, tubeless, no problems.

And you don't want to get a Ventana? It's s sweet frame, alternator drops, plenty of water bottle bosses, pannier mounts fine on the rear.


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## Lars_D (May 24, 2011)

Nurse Ben said:


> Oh, gotcha, this is a fat bike!
> 
> I also use an ICT, same drivetrain set up as you but 10sp; I assume you're doing 9sp to keep things skinny and not have tire to chain contact.
> 
> ...


The Ventana looks sweet, but I really enjoy the process of building full on customs. Plus, this may be a bit lighter at the end of the day (38 lbs according the my preliminary build list).


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## Erichimedes (Jul 30, 2010)

Nice, it sounds like you're homing in on exactly what you want. Should be a really fun bike. I didn't realize you (taller one) were the stoker until you mentioned it. I really want to build us a tandem that is dedicated to me being in the back someday. I think it would be pretty cool. The only other thought I would have is to do a 1x10 instead of 1x9. I have a 1x9 on my mountain bike and sort of wish I had that extra low gear the 1x10 offers. That being said, we run Rohloff on our tandem and I love it.

Be sure to post pics when it arrives!

Also, Nurse Ben, which Ventana offering is that? I don't know if I've seen one.


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## Sanchofula (Dec 30, 2007)

Erichimedes said:


> Also, Nurse Ben, which Ventana offering is that? I don't know if I've seen one.


The El Jefe, a tandem version of the El Gordo fat bike.

I love it, but it would love it even more if it was full suspension!


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## Lars_D (May 24, 2011)

The frame build is in process, but I am still pondering the front fork. The options seem to be either the Ice Cream Truck fork (steel) or the Whisky #9 fat fork (carbon, with no rider weight limit). I am really torn. Any thoughts?


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## Lars_D (May 24, 2011)

The first part has arrived.


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## Lars_D (May 24, 2011)

Wheels are ready. Front is an 80mm Rolling Darryl rim laced to an SP PD-8x dynamo hub with spacers by MTB Tools to allow compatability with a 150mm fat fork. Rear is a 100mm Clown Shoe rim laced to a 197mm 9Zero7 hub. I used conventional spokes and brass nipples front and rear. The tires are smooth Black Floyd tires with Mr Tuffy flat protectors. The rim strips are reflective orange backed with duct tape and 3M tape which should allow a tubeless setup once we have done a few shake down rides. Rear cassette is a SRAM 10-42, 11 - speed. Front disk is 203mm, rear is 160mm.


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## ki5ka (Dec 17, 2006)

.


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## dbhammercycle (Nov 15, 2011)

Lars_D said:


> The frame build is in process, but I am still pondering the front fork. The options seem to be either the Ice Cream Truck fork (steel) or the Whisky #9 fat fork (carbon, with no rider weight limit). I am really torn. Any thoughts?


This looks like a really cool project.

I think the only potential advantage to ice cream truck fork would be braze-ons for cages or racks, but I haven't compared a-c, rake, etc. Obviously the Whiskey fork will be lighter.


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## PMK (Oct 12, 2004)

My opinion on the 160 rear disc, simply too small and as good as you find the front being a 203, you still need more rear brakes. Regardless of the teams weight, the tires have to much inertia and grip. 

No doubt your design and build, can always be changed out later to a larger diameter, however since it is a custom build, I would consider designing the brake caliper mount and supporting structure to use the smallest caliper adapter onto the largest frame mounts. This is similar to how they build some of the high performance forks where they require a 160 caliper mount to run a 203 disc. Much better feel and less flex.

Your call and reasoning to run the 160 though.


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## Lars_D (May 24, 2011)

PMK said:


> My opinion on the 160 rear disc, simply too small and as good as you find the front being a 203, you still need more rear brakes. Regardless of the teams weight, the tires have to much inertia and grip.
> 
> No doubt your design and build, can always be changed out later to a larger diameter, however since it is a custom build, I would consider designing the brake caliper mount and supporting structure to use the smallest caliper adapter onto the largest frame mounts. This is similar to how they build some of the high performance forks where they require a 160 caliper mount to run a 203 disc. Much better feel and less flex.
> 
> Your call and reasoning to run the 160 though.


Good point about the rear brake. I'll increase it to 203 to match the front. As for as making the mounts bigger and the adapter smaller, I think it's too late for that but I'll check. Thanks for the advice.


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## deuxdiesel (Jan 14, 2007)

Lars_D said:


> The frame build is in process, but I am still pondering the front fork. The options seem to be either the Ice Cream Truck fork (steel) or the Whisky #9 fat fork (carbon, with no rider weight limit). I am really torn. Any thoughts?


When I built our fat tandem, the fork was the one place I wouldn't compromise. I had Walt build us one that was tandem rated and capable of handling all tire sizes.
He was even able to build the Pugsley offset into it. The price was only slightly more than a carbon fork, and inspires far more confidence.


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## Lars_D (May 24, 2011)

deuxdiesel said:


> When I built our fat tandem, the fork was the one place I wouldn't compromise. I had Walt build us one that was tandem rated and capable of handling all tire sizes.
> He was even able to build the Pugsley offset into it. The price was only slightly more than a carbon fork, and inspires far more confidence.


Thanks for the response.


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## bugshield (Jun 22, 2012)

Looks like an interesting build! 

I am thinking about a Gran Jefe build (15x150mm front axle) but would like to run a dynohub. 

I'll be interested to see how your adapters work out. Son's 'tandem rated' hub is a 100mm QR hub. Were you able to find a tandem rating or positive experience reported on the SP hub?


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## Lars_D (May 24, 2011)

bugshield said:


> Looks like an interesting build!
> 
> I am thinking about a Gran Jefe build (15x150mm front axle) but would like to run a dynohub.
> 
> I'll be interested to see how your adapters work out. Son's 'tandem rated' hub is a 100mm QR hub. Were you able to find a tandem rating or positive experience reported on the SP hub?


I have had good results with the sp pd-8x in pretty extreme use with adapters. Between its sold internal axle and the 15mm thru axle, I am confident it will hold up.


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## Lars_D (May 24, 2011)

The frame is ready and will be on its way soon...


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## Okayfine (Sep 7, 2010)

Pretty frame!:eekster:


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## Erichimedes (Jul 30, 2010)

Lars_D said:


> The frame is ready and will be on its way soon...


Looks gorgeous! So don't keep us all hanging on the edge of our seats, who built that thing?


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## Lars_D (May 24, 2011)

Some more pictures...


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## PMK (Oct 12, 2004)

Erichimedes said:


> Looks gorgeous! So don't keep us all hanging on the edge of our seats, who built that thing?


My first guess is Quiring

Quiring Cycles | Custom Cycles Since 1999


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## Lars_D (May 24, 2011)

The frame weight is about 2,900 grams.


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## Okayfine (Sep 7, 2010)

Or, a little more than my pair of WTB 2.5 Dissent tires :eekster:


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## Q'sMom (Oct 29, 2006)

PMK -- I don't think so. The yoke is not what he uses and welds???


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## PMK (Oct 12, 2004)

I know Quiring does odd stuff too. No idea then if it is not them.


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## Lars_D (May 24, 2011)

Almost done...


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## Lars_D (May 24, 2011)

Done


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## Lars_D (May 24, 2011)

After a short ride...


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## Lars_D (May 24, 2011)

Erichimedes said:


> Looks gorgeous! So don't keep us all hanging on the edge of our seats, who built that thing?


A mainland China company called HFT built the frame to my specifications. It was powder coated in Anchorage where I live. Here is a link to an Alibaba ad featuring my frame as an example of HFT's work.

https://wholesaler.alibaba.com/prod...60461240947.html?spm=a2700.7724838.0.0.cseqpU

The project was a true international effort that I assembled in Anchorage. Parts included: English rear seat and cranks, American seat posts and bottom brackets, German front tire (and lighting when I get around to it), etc.


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## Erichimedes (Jul 30, 2010)

Lars_D said:


> A mainland China company called HFT built the frame to my specifications. It was powder coated in Anchorage where I live. Here is a link to an Alibaba ad featuring my frame as an example of HFT's work.


Woah! Didn't see that one coming.


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## ds2199 (Sep 16, 2008)

What is the Head Tube angle? I'm not sure if it is just the photo or the fork, but that looks pretty slack, no?


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## Lars_D (May 24, 2011)

ds2199 said:


> What is the Head Tube angle? I'm not sure if it is just the photo or the fork, but that looks pretty slack, no?


Good question. It is supposed to be 70.5. But it looks (and handles) like it is slacker than that. I'll try to measure it.


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## PMK (Oct 12, 2004)

ds2199 said:


> What is the Head Tube angle? I'm not sure if it is just the photo or the fork, but that looks pretty slack, no?


Agree, it has a lot of axle offset and looks like modern day 67 degree headtube angle.


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## Lars_D (May 24, 2011)

PMK said:


> Agree, it has a lot of axle offset and looks like modern day 67 degree headtube angle.


When I initially test rode it, I had smooth 3.7 inch Black Floyd tires on it and the self-steering was really bad. I switched to a Schwalbe Jumbo Jim in front and resolved 90% of the issue. I'll order another Jumbo Jim for the rear come payday and see if that completely resolves the steering issues. If not, I may go with a shorter fork with a bit less offset.


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## PMK (Oct 12, 2004)

Lars_D said:


> When I initially test rode it, I had smooth 3.7 inch Black Floyd tires on it and the self-steering was really bad. I switched to a Schwalbe Jumbo Jim in front and resolved 90% of the issue. I'll order another Jumbo Jim for the rear come payday and see if that completely resolves the steering issues. If not, I may go with a shorter fork with a bit less offset.


No doubt you can test various setups, and often reach a best compromise. Unfortunately, that approach still may not give the best results without some luck. Myself, I would put the numbers to paper and see how the key dimensions for headtube angle, Axle to crown race and trail plot before spending money.

So much of good handling revolves around the magic numbers. I know the tire made it better. Thing is the tire may have been better could be simply masking poor or great geometry.

The front end has a Cannondaleish slack headtube with excess offset that makes for a lot of wheel flop, abrupt weight transfers in to the bars beyond a certain turning parameter or lean angle, and very heavy low speed handling that really works the captain.

All the best with it and I hope the different tire and / or fork dial it in.


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## Lars_D (May 24, 2011)

PMK said:


> No doubt you can test various setups, and often reach a best compromise. Unfortunately, that approach still may not give the best results without some luck. Myself, I would put the numbers to paper and see how the key dimensions for headtube angle, Axle to crown race and trail plot before spending money.
> 
> So much of good handling revolves around the magic numbers. I know the tire made it better. Thing is the tire may have been better could be simply masking poor or great geometry.
> 
> ...


The head angle measures to 67.5 degrees, with a 51mm offset fork and a 740mm tire diameter that equates to around 100mm of trail, which is about right for a fat bike (but maybe not for a fat tandem?). I do think the steering issue was tire-related since the first front tire (a black floyd tire) is notorious for self-steering and I replaced it with a slightly larger diameter tire, which would have made the head angle slacker but in fact greatly improved the handling.


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## PMK (Oct 12, 2004)

Lars_D said:


> The head angle measures to 67.5 degrees, with a 51mm offset fork and a 740mm tire diameter that equates to around 100mm of trail, which is about right for a fat bike (but maybe not for a fat tandem?). I do think the steering issue was tire-related since the first front tire (a black floyd tire) is notorious for self-steering and I replaced it with a slightly larger diameter tire, which would have made the head angle slacker but in fact greatly improved the handling.


Aren't most fatbike singles placing more of the center of mass towards the rear axle or over the rear axle in an effort to keep the front end with a lighter feel? By doing this they get away with slack angles and excessive amounts of trail since the weight jacking and flop effect are minimized with the mass over the rear. All the best with it.


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## Lars_D (May 24, 2011)

PMK said:


> Aren't most fatbike singles placing more of the center of mass towards the rear axle or over the rear axle in an effort to keep the front end with a lighter feel? By doing this they get away with slack angles and excessive amounts of trail since the weight jacking and flop effect are minimized with the mass over the rear. All the best with it.


We'll see how it goes. First step is a matching rear tire which should steepen the head tube angle a bit and hopefully clear up the rest of the self steer.


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## Johnbonn (Apr 7, 2015)

Lars-D
How is it working out. We are looking into putting together a fat bike tandem and looking for advice. Any to provide? What type of riding are you doing with it? Do you know if you can run 29 + tires on 29er rims? Any additional pictures? 
Thank you


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## Johnbonn (Apr 7, 2015)

PMK
You mention magic numbers, please explain. I too would like to get built a fat tandem frame. There seems to be a lot of people talking about how fast the single frame builders are learning from trial and error I believe the tandem builders are farther behind, not as many builds. Any help and thoughts would be greatly appreciated. Ideally I would like to be able to run 26" and 29+ tires on it. 
Thank you


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## Lars_D (May 24, 2011)

Johnbonn said:


> Lars-D
> How is it working out. We are looking into putting together a fat bike tandem and looking for advice. Any to provide? What type of riding are you doing with it? Do you know if you can run 29 + tires on 29er rims? Any additional pictures?
> Thank you


It seems to be working fine. I did put a shorter fork on and an angleset head set which really helped with the handling. I think the steering angle is now closer to about 70 degrees which feels about right. We mostly use it for recreational riding. I don't see any benefit to 29+, so I don't know if they'd fit. We can easily go 15-20mph with fat Jumbo Jim tires.


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## Lars_D (May 24, 2011)

Here is another pic.

Sent from my SM-G900V using Tapatalk


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## Lars_D (May 24, 2011)

Lars_D said:


> It seems to be working fine. I did put a shorter fork on and an angleset head set which really helped with the handling. I think the steering angle is now closer to about 70 degrees which feels about right. We mostly use it for recreational riding. I don't see any benefit to 29+, so I don't know if they'd fit. We can easily go 15-20mph with fat Jumbo Jim tires.





Lars_D said:


> Here is another pic.
> 
> Sent from my SM-G900V using Tapatalk












Sent from my SM-G900V using Tapatalk


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## Johnbonn (Apr 7, 2015)

Anything you would do differently if you did it again? How is the quality of the welds? Why did you powder coat it being titanium? How is it holding up?


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## Lars_D (May 24, 2011)

Johnbonn said:


> Anything you would do differently if you did it again? How is the quality of the welds? Why did you powder coat it being titanium? How is it holding up?


The quality of the welds and build are excellent. I have five frames from HFT and all of them are extremely well done. The only issue I have had relates to the steering angel. The drawing had a 485 a/c suspension fork in it with a non-tapered steering tub and a head angle of 70 degrees. When I built up the bike I used a rigid fork with a tapered steering tube. The effect was to slack out the headtube angle out quite a bit. This introduced extremely sluggish steering. Using a 468 ac fork and an angleset headset fixed most of the problem, but if I had it to do again I would have had it built with a 71 degree head angle based on a rigid fork with a tapered steering tube. As to powder coating, my wife's favorite color is orange.


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