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Discussion Starter · #1 ·
Hi there,

I have been looking at the subjects of all Forums and wonder if this is the best place for my question but be kind on me, this is my first post here.

My son has a Specialized Hot Rock 20 and some parts are starting to wear out. I wonder if it's possible to upgrade the drivetrain. The standard setup has a six speed Shimano Tourney rear derailleur and I wonder if I can change the hub for a 8/9 speed Shimano XT and put on a 8 speed cassette with a SRAM X5 8-speed gripshift and for example a X7 rear derailleur.

I did some measurement on my own bike and I guess the rear derailleur will be fairly close to the ground when it's in the lightest gear (looking at for example 11-30 or even 11-32). The Tourney cassette is a mere 14-28, which doesn't work for climbing hills

I am not sure if there is a suitable chain that works on the standard chainring that's apparently fixed to the crank.

I am also going to change the bottom bracket. The cups that hold the balls in the original bottom bracket are completely gone. Since these bikes still have the old fashioned square axles, I had hoped to find a cheap Ti bottom bracket in the size 68-128 mm and save some weight but I guess that's not going to happen :-(

If I rather should post this question in a different forum, please let me know.

Kind regards,

Clemens
 

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My son has a Hotrock 20 as well, I've done some minor upgrades such as changed to 7 speed triggers and a 14-28 freewheel, but as you said, that's not low enough. I've just ordered a megarange 14-34 freehub. The challenge is the derailler has to be changed as well as the chain as it's too short. After this, I'll hold tight. I have a new 14" Sette Reken about the same size as a Performance Access frame waiting to build. I am going to lace up some 24" in wheels to start, then he'll get 26" wheels when he's a bit older. He's 7 (8 in August when he gets it) and right now, he's just over 48". I built a similar 14" Reken w/ 26 inch wheels for a friend last year, his son was around 53".

My son rides singletrack with me all the time and the Hotrock has been a good bike to help him grow. Since they grow so fast, it does not make sense to throw too much money at it. His is just a year old now and he should be off it by the fall. I had considered lacing up 20" wheels on good hubs to get a cassette on, but held out for the Reken...it was hard though.
 

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turtles make me hot
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I'm currently changing the one x six on my son's Gary Fisher Precaliber to a 1 x 8 XT trigger. Currently waiting for a rock ring and a rim for the new rear hub. He had 34 in front and his biggest rear cog was 28. I e bay'd an 11-32 8 speed cogset.
Also swapped the bottom bracket and a Sinz crankset with a little more length.
 

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Discussion Starter · #4 ·
Thanks for the replies, I really appreciate.

I have two boys, the oldest has the bike for almost 2 years now and it's still in pretty good shape. I will start by swapping the bottom bracket, pedals, handlebar grips and brakes. When he outgrows the bike, I can pass it to the youngest, who now has a Hot Rock 16. This way, the investments in the Hot Rock 20 are in my eyes well spent!


Kind regards,

Clemens
 

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In that case, I'd agree. My son is the youngest so too much money invested would be a waste, but the gearing will help him for the next 6 - 8 months. I'll remove the new parts and replce with the old derailleur, chain, and freehub, that way I only lost $13.99 (freehub cost at Universal). The Deore derailler will be recycled to another build, the chain was a $7 take-off at Jenson ...
BTW, you should be able to pick up a sealed cartridge square taper bb from Jenson for that bike.

Oh, here's the Reken I talked about in my post above:
http://forums.mtbr.com/showthread.php?t=655377&highlight=reken
 

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turtles make me hot
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The wheel guy at my favorite shop finished the rear wheel today. I had him do it since the dish was complicated an I'm still finding my way building wheels. It's one of my old XT 8 speed hubs. He laced it to a Velocity Aeroheat rim. Looks awesome and it's way lighter than what came on the bike. The silver hub with black rim and black spokes looks even better than I thought. I'll be lacing up the front tomorrow. Same deal but on a Ringle Bubba Hub. The Spot chainring protector is on the Sinz Cranks and I picked up a frame mounted Jumpstop for the inside of the chainring. My son picked out Tioga web pedals. They're cool as hell. Little aluminum spider webs. This project is coming along nicely. Only problem is, he's my youngest, so once he outgrows this bike, I either have to sell it at a loss or save it until one of my older kids has kids.
I don't normally look at things this way, but Cing's reply made me realize this.
 

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RSabarese said:
My son has a Hotrock 20 as well, I've done some minor upgrades such as changed to 7 speed triggers and a 14-28 freewheel, but as you said, that's not low enough. I've just ordered a megarange 14-34 freehub.
I just picked up a Hotrock 20 off of Craigslist today. I have a trigger shifter ready to go for it, but wasn't sure if a 7 speed freewheel would fit in the place of the 6-speed. It looks like there's enough clearance. Any advice?
 

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It works good. The only exception is pedaling backwards when on the smallest cog. The chain somwhat jumps atound trying to get to gear 6, but other than that, it's great. I originally put a 14/28 on from Jenson, but my little dude needs more climbing power. I just ordered a 14/34 from Universal. If all you want to do is put triggers and 7 speed, go 14/28 as 14/34 is requiring me to change the derailler and chain as well (not long enough). I have spare derailluers and chain, so when he's done with it on the Hotrock, it will go back to 14/28 and be given to a family member.
 

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Discussion Starter · #10 ·
Today I ordered the Sinz cranks and I will start gathering the other necessary pieces if I feel confident that everything is going to fit.

I do have one question: will a short cage derailleur be sufficient for a 11-34 cassette with only 1 chain ring?

By the way, here are a few pictures of the upgrades I installed last Monday:



















Kind regards and have a good weekend!

Clemens
 

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My son climbed two sandy hills he was previously never able to make before. The longer cranks and 11-32 cassette made all the difference. I think a short cage should work on a 1x8.
 

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I put a 14/34 freewheel, new chain, and Deore M510 Long cage on my son's Hotrock 20 2 weeks ago. It works fine, but the idler gear hits the freewheel when back pedaling. IMHO, I think the derailleur hanger is shorter than a normal mountain bike, so even though it's a long cage, it's still too close. However, he climbs better so I'm leaving it, he get's a new Sette Reken 14" for his B-Day in August (I build up 24" disc wheels to keep the stand over low).
 

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Discussion Starter · #15 ·
Thanks for the answers about the derailleur. In another topic I read that 110 mm 5-bolt parts are easy to come by. My favorite online bike shop however doesn't have so much parts available in this size. I did find a 34 teeth NC-17 chain ring and a Race Face bash guard. I asked them if they can be combined on the Sinz cranks this morning. Maybe somebody here can put my mind at ease?

Kind regards,

Clemens
 

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Discussion Starter · #18 ·
Today, the chain ring, bash ring and bolts arrived. This is going to look extremely good! Here are a few pictures I just took of the parts before mounting them on the bike:







Kind regards,

Clemens
 

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Discussion Starter · #19 ·
Little update: for the Sinz cranks, the standard bottom bracket of 128 mm was way too big. Whenever my son spinned the pedals backwards on the first gear, the chain came off.

I measured everything carefully and got a few tips in another topic I started about bottom bracket size and today I installed the 113 mm BB. Works like a charm.



Other good news: all other parts are in too and I have my LBS build the wheels. They will be ready end of next week and then I can do the full upgrade to 9 speed.

I also found back my old Titec Hell Bent handlebar and once I locate the tube cutter, I am going to swap the steel bars. That will probably save at least 300 grams :)

Kind regards,

Clemens
 

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Discussion Starter · #20 ·
Today I finally got a call from my LBS to tell me the wheels were built. I picked them up early this evening and they sure look great:



Unfortunately, the new wheels are not lighter than the old ones. The new ones have 36 spokes instead of 32 and the rims are 5 mm wider.

This evening, I installed the front wheel and when re-adjusting the brake pads, I dropped a steel washer ring. It took me more than half an hour to finally find it. It had bounced off more than 2 meters from where I was working!

When the front wheel was finally ready, it was too dark to take a picture. I did have a good look at the rear wheel though and noticed that the valve hole is not between two straight spokes but between two crossed ones. This is going to be very hard for inflating the tires so I think I will take this wheel back. I payed $ 130 for labor, spokes and nipples and I think that I am entitled to a correctly spoked set of wheels for this amount, what do you think?

Kind regards,

Clemens
 
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