[kickstand]

Just ordered some 145 mm cranks for my little guys bike last night. They are the same length as his mini bmx cranks so I figured that would be a good length, the 165's hit everything imaginable

I swapped his 24" stock fork for a shorter travel 26" fork. It lowered the standover a good bit for him. I think I will run it like this for a year or so. I still need to do something about the seatpost like kntr did. I'll get a pic of him on the bike this weekend to give a reference to you guys for sizing. It's still too big, but he's determined to ride it.

Before:

After:

 

[student]

kickstand, may I ask how tall is your boy? My boy also rides 145 on his mini BMX.

I think the changes you have made should help him. Also what is the amount of travel on the fork pls?
Thanks for sharing the info and pictures.

weedkilla, float and van are an option. Talas are not (for me), I really don't like them. I dont think they are sensitive enough to any small bumps.

 

[Kntr]

kickstand
You can get a used Thompson seat post for pretty cheap. Check PB.

 

[kickstand]

kickstand, may I ask how tall is your boy? My boy also rides 145 on his mini BMX.

I think the changes you have made should help him. Also what is the amount of travel on the fork pls?
Thanks for sharing the info and pictures.

weedkilla, float and van are an option. Talas are not (for me), I really don't like them. I dont think they are sensitive enough to any small bumps.

He is 46" tall. I just ordered the 145mm cranks, don't have them yet.

Fork is a rock shox tora for a 26" wheel, I believe it's a 100mm.

I'll snap a pic of him on the bike today, it's still quite big, but with the few changes I think it will be manageable.


I'd really like to find a 20" rear wheel and see if that would do him any good or if it would lower the bike too much, the trails I intend to take him to are not rocky and are mostly whooped out loamy pine forest type trails, no rocks at all, so I wouldn't be too concerned with the derailuer taking a hit. But I think with as fast as he is going to start growing it's not gonna matter
Thanks Britt, I will take a look on PB.

 

[Kntr]

He is 46" tall. I just ordered the 145mm cranks, don't have them yet.

Fork is a rock shox tora for a 26" wheel, I believe it's a 100mm.

I'll snap a pic of him on the bike today, it's still quite big, but with the few changes I think it will be manageable.


I'd really like to find a 20" rear wheel and see if that would do him any good or if it would lower the bike too much, the trails I intend to take him to are not rocky and are mostly whooped out loamy pine forest type trails, no rocks at all, so I wouldn't be too concerned with the derailuer taking a hit. But I think with as fast as he is going to start growing it's not gonna matter
Thanks Britt, I will take a look on PB.

A 20" in the back will not work. The bike is low to the ground already.

I'm thinking a 26" front wheel and a 170 air Lyric next year. Then she will quit hitting rocks with her pedals. The small HT pedals made a huge difference, but she still hits them once in awhile.

 

[student]

26" front wheel and 170 fork should be good for your girl, as she is fits the bike well now.

I don't think the 20" rear wheel is a good idea either, should he bottom out the rear suspension, he could even hit the chainring, and would create all sorts of other geometry issues. May be try the offset bushes, I reckon it may lower the bike about 1/2 an inch, and be lot cheaper then new wheel? And should work ok with your shorter cranks.

I am interested to see some of the action pictures of your boy kickstand, he is very similar height to my boy, so keen to see how he fits. Thanks

 

[epic]

Gromhit in the house!

 

[kickstand]

Current fit, took these today, you can see how badly he needs shorter cranks

Nice pants

 

[student]

Thanks kickstand for the pictures, yes I agree, he does need shorter cranks.
When you install them, can you take some more pictures please?
How does he find getting on and off the bike ATM?
And does he ride the bike off road at all?

Thanks

 

[kickstand]

Well, he gets on and off the bike on his own, but it takes some work for him to get a leg over it and position the pedals correctly and get started. But he finds a way, he's one of the most determined kids i've seen. He doesn't let a challenge stand in his way.

We haven't ridden it on the trails yet because he has other bikes that are a better fit. However, the saturday before father's day I plan on taking him to the bike park and getting some lift riding in. He really wants to take his hardtail because it is easier to get on and off and fits a bit better.

Either way I will get some go-pro footage and some pictures.

 

[Kntr]

My daughter has long legs. Here is a pic of her riding her bike in front of the house when she was 6yo.

She did fit better on her 20" though.

 

[student]

Well, looks like my boy could even fit on the Gromhit this year, wow.
But I am already in process of building him nice Hotrock 20 for this season, it will be easier to manoeuvre for him off road, and learn new skills on it. It should also be easier for him manhandle the bike too (or boyhandle? ). Only shame he will have the bike probably for less then 10 months. May be he can have it later as his DJ/skatepark bike. I'll put up some pictures when it's ready.

And with the tips from this great thread, I should be able to build him pretty sweet Gromhit for next season, I can't wait!

 

[epic]

Well, our Gromhit arrived yesterday. It is out cruising the neighborhood right now. What can you guys tell me about tuning the fork? What is in there? The damping knob works, which is nice, but I have about 2lbs of air in each side, and it's a little stiff. I'm guessing if I pull off those air valves, I'll find a coil spring or two?

btw - whole bike is 33lbs, one tire = 750g, pedals are 550 or so. steel chainguide, and chainring and cranks/BB look awfully heavy too. I'm not too worried about the weight though, it's mostly for lift-served. anyway.

 

[kickstand]

kntr has said you can pull the coils out of the fork

 

[Kntr]

Pull the spring out of the fork and run it on just air. The fork actually feels pretty good. Marzocchi told me it was fine to do this.

I changed pedals, seat post, seat, handlebars, and tires and got the bike down to 31 lbs.

edit: For anyone looking for a Gromhit there are a few on PB for sale. One looks like its in pretty good shape still.

 

[ChrisKring]

The guy on Pinkbike doesn't want to ship. Where else are you guys finding these bikes?

 

[Kntr]

The guy on Pinkbike doesn't want to ship. Where else are you guys finding these bikes?

Pinkbike is the only place Ive seen them. Ask the guy if he will take it to a bike shop and have them ship it.

There are a few on PB.

http://www.pinkbike.com/buysell/list/?q=grom+hit&category=0&pmin=&pmax=&region=3

 

[kickstand]

The guy on Pinkbike doesn't want to ship. Where else are you guys finding these bikes?

Chris I found mine by starting a thread here actually. It came from Idaho. There was also a guy over in Grand Rapids area that had one when I was looking, he had it listed on craigslist. How old is your son/daughter? We should try to get them together up at boyne one weekend.

 

[ChrisKring]

He's almost 9. Rides moto but is tentative on a bicycle. Was thinking that if he had some suspension that he might push it a little more.

Boyne would be good sometime. Might make it this weekend for the race but I'll be solo if I make it since we have something planed for Saturday evening.

 

[kickstand]

I won't be there this weekend, I am heading to snowshoe, but I am gonna take my son up on the 16th (saturday before fathers day).

His 145mm cranks came today, just need a new chainring.

 

[Kntr]

There are quite a few Grom hits on PB now. Search gromhit and grom hit. A couple in Canada look like they are in good shape.

 

[kickstand]

damn cranks don't fit, the spline count and diameter is correct, but the splines on the BB are too "thick" to fit in the female splines on the cranks.....is there two types? do I need a different BB or do I just need to stop being a pussy?

 

[Jim Mac]

what cranks to what bb?

 

[kickstand]

>ISIS

What does ISIS mean?

The ISIS Drive is an open standard for splined bottom bracket interface. It was designed by Race Face, Chris King and Truvativ as an alternative to Shimano's Octalink. As such, the two are not compatible. Any ISIS crank will fit any ISIS bottom bracket, regardless of the manufacturer. They are not compatible with Shimano however.

What's the difference between ISIS and square-taper systems?

ISIS technology is the new standard for strength, stiffness, and performance. The spline/flute system allows for a tight, creak-free set-up that keeps everything sandwiched in place to eliminate movement and ensure reliable shifting. The square taper system is still strong and reliable, however, with the ISIS system is the platform for numerous excellent products based on the aforementioned facts.

Cranks are SINZ 145 mm ISIS cranks

http://compare.ebay.com/like/320604931780?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar&_lwgsi=y&cbt=y

BB is a Truvativ Howitzer Power spline

***edit***

Found my answer

TruVativ Power Spline Bottom Bracket. Proprietary spline design popular as OE spec with many moderate-priceTruVativ cranks. Proprietary spline design popular as OE spec with many moderate-priceTruVativ cranks Please note:This item is NOT ISIS Compatible Item Specifications BB Shell Width 68 mm Weight 305 g BBThreadType English Spindle InterfaceTypeTruVativ Power Spline

That would have been good research to do, I just assumed it was an ISIS spline. Can the spindle be replaced easily or do I need to replace the entire bottom bracket? Finding a powerspline crank that is shorter is probably a PITA?

Oh well, guess you learn something new everyday

 

[UiUiUiUi]

you will need a new bb.

 

[kickstand]

damnit.

Kntr what cranks did you use? did you also switch bottom brackets?

I love learning this ****, I really do.

 

[Jim Mac]

I was looking at the Dan's comp catalog, and I think that Sinz have their own BB for those cranks?? maybe a standard (old fashioned) cartridge non external ISIS BB? Might be this one:
http://www.danscomp.com/products-PARTS-BottomBrackets/456052/Sinz_ISIS_Cartridge_BB.html

 

[kickstand]

I saw that, next question is trying to remember (while I'm at work) if the bike has ICSG mounts or if the chain guide is BB mounted, will it work with a BB like that if it is BB mounted? I don't see anything to sandwich it into place.

Now I know why the bike shops just tell me to leave when I ask them to do something like this for my kids bike

 

[ChrisKring]

I saw that, next question is trying to remember (while I'm at work) if the bike has ICSG mounts or if the chain guide is BB mounted, will it work with a BB like that if it is BB mounted? I don't see anything to sandwich it into place.

Now I know why the bike shops just tell me to leave when I ask them to do something like this for my kids bike

huh? Post a picture.

If it is bottom bracket mounted, just leave it that way and get the appropriate bottom bracket.

 

[weedkilla]

Yes, you can use a bb mount chainguide with that bb. You can see the flange on the right hand side on the picture posted earlier.
Yes, the gromhit has iscg mounts. I think iscg old.

 

[ChrisKring]

There are quite a few Grom hits on PB now. Search gromhit and grom hit. A couple in Canada look like they are in good shape.

Thanks. I was searching "gromhit" and only finding a couple.

 

[kickstand]

huh? Post a picture.

If it is bottom bracket mounted, just leave it that way and get the appropriate bottom bracket.

I will check it out when I get home, I am terrible with bike lingo and trying to explain things.

 

[kickstand]

Yes, you can use a bb mount chainguide with that bb. You can see the flange on the right hand side on the picture posted earlier.
Yes, the gromhit has iscg mounts. I think iscg old.

Roger that, if it has frame mounts I am golden, or, if like you said that lip is there I can go that route as well. Thanks.

 

[kickstand]

Thanks. I was searching "gromhit" and only finding a couple.

I don't know what the thoughts are on the stinky 2-4, but I considered one of those as well. Seven Springs had 2 for sale last year, they wanted $500, they were in rental bike condition.

 

[Kntr]

damnit.

Kntr what cranks did you use? did you also switch bottom brackets?

I love learning this ****, I really do.

I left the stock ones on. She just dealt with them being too big for a couple years.

 

[thad]

I was looking at the Dan's comp catalog, and I think that Sinz have their own BB for those cranks?? maybe a standard (old fashioned) cartridge non external ISIS BB? Might be this one:
http://www.danscomp.com/products-PARTS-BottomBrackets/456052/Sinz_ISIS_Cartridge_BB.html

FSA Platinum Pro is a nicer BB, lighter, $44.
http://www.bikeman.com/CR4991.html?utm_source=GoogleBase&utm_medium=GoogleBase&utm_campaign=GoogleBase

$22 seat / post combo slams lower than any other post seat combo, and is super light 250g.
http://www.danscomp.com/products-PARTS-SEATPOSTCOMBO/470197/Cult_Occult_Seat|Post_Combo.html
$5 shim.
http://www.amazon.com/Sunlite-Alloy-Seat-Post-Shim/dp/B002ND9FMQ

 

[kickstand]

Yes, the gromhit has iscg mounts. I think iscg old.

Correct. Just couldn't recall from work. My buddy has an ISIS bb laying around, so we should be all set.

 

[epic]

You'd better check and see if it is 68/73mm or 83mm and plan accordingly.

 

[kickstand]

ok update.

The truvativ BB was a 68x130/135 ish.

ISIS BB's wide enough to space the cranks out far enough to clear the rear suspension are hard if not impossible to come buy.

Ironically the bottom bracket (square taper) on my son's mini was wide enough (Spindle length) and the isis bracket and cranks fit into his mini bmx, so luckily I was able to make the swap pretty easily.

So he is all set with some 140 cranks on the DH, some 145's on the mini, and the original cranks and BB ready to swap onto the big hit when he grows a bit.

We're going for our first day of lift riding tomorrow, so i'll get some go pro to share.

Thanks for the help guys.

 

[sbabuser]

$22 seat / post combo slams lower than any other post seat combo, and is super light 250g.

I tried one of those on my bmx - not very comfortable, and too much rearward tilt, IMO.