# 6 speed to 8 speed conversion.



## regiobike (Apr 23, 2017)

Hi there guys, well we love to ride with my wife and 2 sons. I like to build my bikes but honestly im lost on the "kids" area lol. My 6 years old son is getting really interested on MTB, he started just a few months ago and he already love pump racks, small jumps and climbs. We have already a good frame but normal mortal shimano 6 speed with 28T in the back.

Im trying to figure out what do i need to make his 20" bike 8 speed with 34T on the back, he hates the 6 speed grip shifter, too hard to use. For what i see this is what i have in mind:

Shifter:
https://www.amazon.com/Shimano-Acer...ords=Shimano+Altus+Rapid+Fire+8+speed+Shifter

rear derailleur:
https://www.amazon.com/dp/B005CMUQU...colid=ETE7JMNLMN0Q&psc=1&ref_=lv_ov_lig_dp_it

Cassette:
https://www.amazon.com/dp/B005DTX1V...colid=ETE7JMNLMN0Q&psc=1&ref_=lv_ov_lig_dp_it

in the front he has a 42t chain ring with 140mm cranks

Any advice will be amazing!!!.


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## Sparkman999 (Dec 19, 2017)

There's a good chance the rear cogs are a freewheel assembly and not a freehub and cassette. If you're not sure how to check, take the wheel off and take a picture so others can help. The Park Tool website has some great info on how to tell the difference: 
https://www.parktool.com/blog/repair-help/determining-cassette-freewheel-type

If it is a cassette, I'm not sure if an 8 speed and 6 speed cassette fit on the same freehub. It's likely that it won't fit. What kind of bike is it? You may be better off getting a different bike, rather than upgrading this one.

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## regiobike (Apr 23, 2017)

confirmed freewheel.


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## Sparkman999 (Dec 19, 2017)

You may be able to convert:





,

but it may be more effort than it's worth


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## GrayJay (May 16, 2011)

There are 8-speed threaded freewheels that would work with your existing wheel
https://www.niagaracycle.com/catego...Ur5GnwnUViXH5FjzyW2E0DpjS_wINvc4aAr6XEALw_wcB
You would need to verify frame dropout spacing, add axle spacer to the drive side and re-dish the wheel to re-center. Alternative is to build a new wheel with a cassette hub (possibly re-use the rim and spokes).

You probably do not need a new derailleur for 8-speed conversion but a narrower chain would be advisable.

42t front chainring is really tall, you would probably be better off to change the chainring and/or crank as needed to get a smaller chainring.


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## regiobike (Apr 23, 2017)

GrayJay said:


> There are 8-speed threaded freewheels that would work with your existing wheel
> https://www.niagaracycle.com/catego...Ur5GnwnUViXH5FjzyW2E0DpjS_wINvc4aAr6XEALw_wcB
> You would need to verify frame dropout spacing, add axle spacer to the drive side and re-dish the wheel to re-center. Alternative is to build a new wheel with a cassette hub (possibly re-use the rim and spokes).
> 
> ...


What should be a great front chainring #?


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## Crashtestdummee (Sep 14, 2015)

What about putting this on. Not 8 speed , but 7 and it would work with the stock shifter and get you 34T.

https://www.niagaracycle.com/catego...MI-Ij8k_-I2gIVEER-Ch2m-wucEAYYASABEgKtOvD_BwE


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## regiobike (Apr 23, 2017)

Crashtestdummee said:


> What about putting this on. Not 8 speed , but 7 and it would work with the stock shifter and get you 34T.
> 
> %20(SPLA)&utm_medium=cpc&utm_term=People%20Searching%20For%20Bike%20Parts&utm_content=Google%20Shopping&product_id=21045&device=t&loc_physical_ms=9030041&gclid=EAIaIQobChMI-Ij8k_-I2gIVEER-Ch2m-wucEAYYASABEgKtOvD_BwE" target="_blank" class="link link--external" rel="nofollow ugc noopener">https://www.niagaracycle.com/catego...MI-Ij8k_-I2gIVEER-Ch2m-wucEAYYASABEgKtOvD_BwE


The stock shifter is 6 speed. So I will not use the Lower gear?. 34t is a lot of difference for my kid. Will be nice


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## RAKC Ind (Jan 27, 2017)

His kid has a 42t chainring, no need to even care about the rear cause even a 34 isn't going to help much


Need to get a proper crank with replaceable rings or at least one with a 30 or 32t ring on it. 42 is rediculous, sounds like a cheap walmart bike.

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## regiobike (Apr 23, 2017)

RAKC Ind said:


> His kid has a 42t chainring, no need to even care about the rear cause even a 34 isn't going to help much
> 
> Need to get a proper crank with replaceable rings or at least one with a 30 or 32t ring on it. 42 is rediculous, sounds like a cheap walmart bike.
> 
> Sent from my SM-G950U using Tapatalk


Thanks for your comment, what do you recommend for a crank and chainring. Maybe I can change all the group.


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## RAKC Ind (Jan 27, 2017)

I use trailcraft cranks for my kids bikes.

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## Crashtestdummee (Sep 14, 2015)

regiobike said:


> The stock shifter is 6 speed. So I will not use the Lower gear?. 34t is a lot of difference for my kid. Will be nice


If the bike has the Shimano tourney revoshift shifter it is capable of 7 speeds. The seventh position is actually on the shifter dail are just not using it right now because you only have 6 speeds. However, many kids bikes have the Shimano tourney short cage rear derailer which is not capable of using a 34T clog. But a simple swap to the Shimano long cage tourney rear derailleur will fix that.

You will need this rear deraileur to make the 7 speed 34t gear set work. https://www.amazon.com/Tourney-Shimano-Rear-Derailleur-RD-TX55/dp/B00U1U9YQU

Does the rear derailleur on your kids bike have an axle mount or direct mount.


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## Crashtestdummee (Sep 14, 2015)

Actually it looks like you will need to upgrade the twist shifter to this 7 speed model from the 6 speed one you have.

https://www.amazon.com/Shimano-Revo...rd_wg=BWBpd&psc=1&refRID=2CV796B1JMW6BCCNRGJF


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## regiobike (Apr 23, 2017)

What about this freewheel 8 speed hub:

https://www.niagaracycle.com/catego...Ur5GnwnUViXH5FjzyW2E0DpjS_wINvc4aAr6XEALw_wcB

The 8 speed shifter and rear derailleur on my first post.


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## regiobike (Apr 23, 2017)

Crashtestdummee said:


> If the bike has the Shimano tourney revoshift shifter it is capable of 7 speeds. The seventh position is actually on the shifter dail are just not using it right now because you only have 6 speeds. However, many kids bikes have the Shimano tourney short cage rear derailer which is not capable of using a 34T clog. But a simple swap to the Shimano long cage tourney rear derailleur will fix that.
> 
> You will need this rear deraileur to make the 7 speed 34t gear set work. https://www.amazon.com/Tourney-Shimano-Rear-Derailleur-RD-TX55/dp/B00U1U9YQU
> 
> Does the rear derailleur on your kids bike have an axle mount or direct mount.


Here is the pic of the rear


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## Crashtestdummee (Sep 14, 2015)

That is a Kawasaki K20G kids 20 inch bike. Which is a 30 pound steel frame department store bike. Brand new the whole bike sells for about a $100. Do not even try to put an 8 speed setup on that thing. 

The 7 speed gear set I listed earlier is about all that bike is even worth trying. The derailleur on it is a direct mount design and “might” work and the shifters that come on those bikes usually are the 7-speed Shimano Revoshift even if it is just 6-speeds. So you can probably reuse the shifter and a small possibility the rear derailleur. 

Would not put anymore time or money than that. Good luck those Dynacraft Walmart bikes can be a real pain.


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## regiobike (Apr 23, 2017)

maybe that k20G has the same group, this one is a alubike bike, which is a good brand locally, most of their 26+ has slx and xt groups, this is one is 16, the 17+ models comes with 7 speed. The bike is almost new so thats why i was trying to upgrade the bike.


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## Wolfjon (Mar 19, 2011)

Crashtestdummee said:


> That is a Kawasaki K20G kids 20 inch bike. Which is a 30 pound steel frame department store bike. Brand new the whole bike sells for about a $100. Do not even try to put an 8 speed setup on that thing.
> 
> The 7 speed gear set I listed earlier is about all that bike is even worth trying. The derailleur on it is a direct mount design and "might" work and the shifters that come on those bikes usually are the 7-speed Shimano Revoshift even if it is just 6-speeds. So you can probably reuse the shifter and a small possibility the rear derailleur.
> 
> Would not put anymore time or money than that. Good luck those Dynacraft Walmart bikes can be a real pain.


Actually here is the link to that bike. it's made from 7000 series Alum. https://www.alubike.com.mx/k20-boy
Not a Trek or Specialized but it does look better than a dept store bike.


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## regiobike (Apr 23, 2017)

yes thats the one. I considering make this 8 speed and in a year or so get a 24" and get it 1x10" deore. My son is a bit small so a guess the 20" will last 2 years at least.


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## Crashtestdummee (Sep 14, 2015)

I saw that K20 on the frame which is what I have seen on those Kawasaki bikes And thought it was that bike. Looks like alubike is a decent aluminum frame. I have not converted a 6 to an 8 speed freewheel only 6 to 7 speed free wheels so not sure if it will all work together with what you picked. Looks like it will but I will let some of the others chime in on this one.


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## regiobike (Apr 23, 2017)

Just ordered the freewheel 14-34T, Shimano 7 speed shifter, rear der. And I found a 36T chainring locally. We will see how it works.


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