JR Race Bike Tires: 20" pro or 20" mini?

[CAN]

Hey guys,

I have one year of fathering my sons bmxing under my belt. Was hoping you guys can add some wisdom on my sons build. His JR. GT Ultra Box Speed Series Team Issue is in my profile (if you need or want to see). In the pic I have a set of 20 x 1 1/18 light ACS Crossfire rims mounted. Going to try 1.5" treads as this is a small as they get for this size rim. I also have the more common junior style race rim (Sun) with 20 x 1 1/8 treads behind the GT. 

So my question is, which to go with? They both weigh the same.

Crossfire pros: Can ride this bike all the time to become one with it. Better traction on our not so perfect rutted and dusty track (Alot front wheel slide out last season).
Crossfire cons: Wider tread will having more rolling resistance. I will have to move the brake mount 1cm down to accomodate these rims (after, with Paul Motolites, both rims will work).

Sun pros: Slimmer for faster rolling. Larger circumference for more roll per pedal (with exact same gearing).
Sun cons: Less ride time to learn his bike better.

Is there anything I am missing? If I put the proper gear ratio for 1.5 are these rims equal? I think I am missing something since everyone else runs 20 x 1 1/8.

I would prefer to just use one rim and not alternate, as the Pauls brakes are suppose to be widely adjustable but a bit of a pain to do.

As for treads looking to go with this season:
Crossfire: Front, 1.5 Odyssey Overbite, Rear, 1.5 Intense Microknobbys
Sun: Front, 1 3/8 Overbite, Rear, 1 1/8 Microknobbys

Share the wisdom....And Thanks
 

[dialledbikes]

How old is the boy?
Is he small, average or big for his age?

Slimmer tyres will roll faster (quicker accelleration) but grip less and will feel harsher/less forgiving over jumps and bumps.

The Paul brakes are good, but a bit tricky to set up.  Have you considered using Bombshell VPS?

[CAN]

Hey Mike,

He is average build/height. He is 9 this year and is doing light sprint and strength training.

Thanks for the VPS...never seen those before and will definitly prevent frame issues and value.

I actually meant to get the race correct wheels but was misinformed. When they arrived it seemed like a smart way to go for our track, being dusty and rutted. But I would not like to give him too much a disadvantage. Plus we will be hitting other tracks around this year and I do not know thier characteristics yet.

Pauls have the widest range options of about 3". Incase of needed tire swaps.

1.5 inflated outta keep up with a 1 1/8. As long as gearing is correct. I feel I'm missing something still though. Maybe it's just no one else uses the smaller rims.

[Dingobmxer]

The smaller wheel (1.5) will accelerate faster (out of the gate) so may well be worth the advantage?

  DINGO

[CAN]

Hey Dingo...why will a smaller and wider tire be faster than a thinner, larger cirumference tire?

Here is the link to see the crossfires (mounted on bike) and the sun rims (behind the bike) http://www.bmxmuseum.com/bikes/gt_bicycles/10146

[Dingobmxer]

Hey Dingo...why will a smaller and wider tire be faster than a thinner, larger cirumference tire?

Here is the link to see the crossfires (mounted on bike) and the sun rims (behind the bike) http://www.bmxmuseum.com/bikes/gt_bicycles/10146

smaller wheels accelerate faster, bigger wheels keep momentum better its a physics thing but I would keep to the skinnies until he starts jumping enough to potentially wreck them, less rolling resistance

  DINGO

[CAN]

Do you think thinner tires used only when racing, out weighs riding his bike everywhere and understanding his bikes characteristics/handling/etc. better for when he does race?

that doesn't really make sense...try again here. If I stick with the crossfire 1.5, he can ride this bike on and off the track which will give him an advantage technically and overall surpass kids that do not ride their bikes very often and do not understand how their own bike really handles.

whatta ya think?

[Dingobmxer]

set the bike up so he is used to it, if that means 1.5's then so be it, he will be comfortable with the set up which will help him mentally too

  DINGO

[dialledbikes]

At 9, I think you should just encourage him to have fun and enjoy his racing, and not get too caught up in the technical/mechanical side of things, as it will just drive you mad.

For what it's worth, my son rides an off the peg DK Mini with 1&1/8th tyres.

At 9, I think the thinner tyres will be better for him to race on.  Maybe let him practice on the wider tyres, and if he prefers them, keep them on for racing.

I think Donny Robinson used 1&1/8th tyres well into his teens.

[CAN]

I think I can keep the weight at about 13 pounds which is lighter than most..since everyone rides stock agents and redlines around here.

weight + proper gear ratio + traction + bike familiarity should equal a winning combo!

I do know that centrifical force is a big part in acceleration capability. With both wheelsets equalling each other, weight wise and only 1' circumference difference......I think it is a close call.

I think the 20 x 1.5 are the overall best choice.

I hear you mike, on using 1 1/8 as everyone else does. The problem last year was front wheel slide out even with the tire psi lowered. I thought with a slighty wider tread he could prevent this. The crossfires are 1 1/8 but are still the standard smaller diatmeter rim. Expert class does use the same rim size as minis and juniors.

Still up for wisdom if anyone else can see something I can't.

Thanks Mike and Dingo for your input

[AL]

Can.... 
My lads  9 this June...              And   20x 1/1/8ths    are defo the correct wheels /tyre set -up, its what all the kids use  ....   I have a pair of as  new FMF  wheels ,  Hollow spindles, Flip Flop Hub.. ( I think  15+17 freewheels on ?)   Tyres as new...

I can email you pics if you want , but would want £60...  All in  ( Skinny Tyres and Tubes , would be £40 on there own )

PM  me if your interested ...
Cheers

[Moschops]

Unfortunatley there is no compramise in making a race bike fit for use off of the track, a race bike is just that a bike for the race track only, this means you can use the 1 1/8th wheels (which are a must) and make it faster knowing that they will never be bummped up a kerb or slammed into a skate ramp.

This leads to the garage full of bikes senario that most of us will be familar with.

[CAN]

Thanks Guys,

I have decide with your advice to stick with the skinny taller rims. I will use a set for off the track and use a good set strictly for racing. This will enable him to still enjoy and become familiar with his bike (Not jumping or freestyle) and still will have a fast straight set for the races. I still like these crossfire race rims and will be posting on ebay soon, since there is no need anymore.

See ya at the track if you're ever Ottawa racing!