Grom clone tire sizes

kirbo7106 · 08-25-2018, 10:31 PM

I noticed the Hellcat has 120/70-12 tires front and rear while the Vader (and the Honda Grom) have a 120/70-12 on the front and a 130/70-12 on the rear. Some Honda Grom owners are running a 120/70-12 on the front and a 140/70-12 on the rear.

This leads to the question: What is the optimum tire size? Eric Buell ran a 120 on the front and a 180 on the rear. He said that was the optimum sizes. He said that any wider on the front would slow steering down too much. Any wider on the rear would either slow the bike down, slow the steering down or would not help at all.

My first motorcycle, a 1987 Kawasaki Ninja 250, had smallish tires. I was going to go up one size on the rear, but was told that it would actually slow the bike down.

So back to my question, “What is the optimum tire size?”

Chinabike · 08-26-2018, 02:15 AM

I think 120/70 front and 130/70 back is best
i'm might get two 120/70 i don't like the fatty back tire look.
and if you go any bigger on the front it might not clear your fender.

RedCrowRides · 08-26-2018, 10:51 AM

The thing on a 125cc Bike is, you are dealing with very limited HP and Torque as a constant ,and it is a lot more apparent in a small displacement when changes are made that negatively impact dynamics. What i mean is , even a slightly heavier tire ( larger)weighs more ,and it's going to take that much more to drive it. Anything larger / heavier than the absolute minimum needed to maintain adhesion and traction is going to cause issues due to that - addtl drag / resistance due to weight and/or excessive contact patch.With todays amazing tire compounds which allow much better traction / adhesion than even the best tires of even a decade or so ago ,I'd focus on using the smallest ( lightest) tire sizes I could get away with , and balance that by emphasizing the compound selection for the type and style of riding i intended to do .
What I'm saying is a small race compound rear tire will have more "grip" than a much larger tire of a harder compound ,even though the larger tire has more contact area, it isn't going to grip as well due to the overly hard "over road" compound.

So, i tend to agree with Chinabike on 120/70 and 130/70 as tire sizes being pretty much optimal, I'd be more diligent on looking at the weights between tires ,and the compound more so than the size , you just aren't realistically likely to " out power" a small tire on a 125 , like perhaps you would on a Full Size sport bike, when tire sizing can become a much more critical factor.

Anyways that's my take on it ,filtered thru the lens of it's going on a 125cc machine ,it's entirely possible someone will come along and prove me totally wrong ,and/or call me insulting names ,neither of which will be a first time occurrence lol

wlfpck · 08-27-2018, 11:05 AM

Check out Hondagrom.net and check the racing sections. There are a good amount of people that race their groms and some gokart tracks let peole take groms/z125/etc. on them.

My recommendation would be to go with what these guys run. Or something similar. The good thing is you'll be able to see reviews on what people have ran on the groms. Outside of that... I don't have much advice. I'm still running the stock tires.

08-25-2018, 10:31 PM	#1
kirbo7106 Join Date: Feb 2017 Location: Holiday, Florida Posts: 672	Grom clone tire sizes I noticed the Hellcat has 120/70-12 tires front and rear while the Vader (and the Honda Grom) have a 120/70-12 on the front and a 130/70-12 on the rear. Some Honda Grom owners are running a 120/70-12 on the front and a 140/70-12 on the rear. This leads to the question: What is the optimum tire size? Eric Buell ran a 120 on the front and a 180 on the rear. He said that was the optimum sizes. He said that any wider on the front would slow steering down too much. Any wider on the rear would either slow the bike down, slow the steering down or would not help at all. My first motorcycle, a 1987 Kawasaki Ninja 250, had smallish tires. I was going to go up one size on the rear, but was told that it would actually slow the bike down. So back to my question, “What is the optimum tire size?” __________________ Dan-O -2018 Tao Tao HellCat - DOA -2016 Hawk 250 - Kitty Hawk - eBay exhaust, Mikuni carb(120 main/30 Pilot), airbox mod with K&N filter, digital cluster, total LEDs, 17/45 sprockets, RK chain, Shinko 244 tires, trunk, aftermarket levers, burrito tube, skid plate, Sargent Cycle Seat... -2003 HD Sportster 100th Anniversary -1999 Buell X-1 Lightning - Race kit, Buell Seat
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08-26-2018, 10:51 AM	#3
RedCrowRides Join Date: Jun 2018 Location: Florida Posts: 759	The thing on a 125cc Bike is, you are dealing with very limited HP and Torque as a constant ,and it is a lot more apparent in a small displacement when changes are made that negatively impact dynamics. What i mean is , even a slightly heavier tire ( larger)weighs more ,and it's going to take that much more to drive it. Anything larger / heavier than the absolute minimum needed to maintain adhesion and traction is going to cause issues due to that - addtl drag / resistance due to weight and/or excessive contact patch.With todays amazing tire compounds which allow much better traction / adhesion than even the best tires of even a decade or so ago ,I'd focus on using the smallest ( lightest) tire sizes I could get away with , and balance that by emphasizing the compound selection for the type and style of riding i intended to do . What I'm saying is a small race compound rear tire will have more "grip" than a much larger tire of a harder compound ,even though the larger tire has more contact area, it isn't going to grip as well due to the overly hard "over road" compound. So, i tend to agree with Chinabike on 120/70 and 130/70 as tire sizes being pretty much optimal, I'd be more diligent on looking at the weights between tires ,and the compound more so than the size , you just aren't realistically likely to " out power" a small tire on a 125 , like perhaps you would on a Full Size sport bike, when tire sizing can become a much more critical factor. Anyways that's my take on it ,filtered thru the lens of it's going on a 125cc machine ,it's entirely possible someone will come along and prove me totally wrong ,and/or call me insulting names ,neither of which will be a first time occurrence lol __________________ 2001 Mustang GT 2004 Sportster 2018 VADER 2020 Orion RXB250L
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08-27-2018, 11:05 AM	#4
wlfpck Join Date: Mar 2018 Posts: 249	Check out Hondagrom.net and check the racing sections. There are a good amount of people that race their groms and some gokart tracks let peole take groms/z125/etc. on them. My recommendation would be to go with what these guys run. Or something similar. The good thing is you'll be able to see reviews on what people have ran on the groms. Outside of that... I don't have much advice. I'm still running the stock tires. __________________ 2020 Honda Grom 2017 Icebear Fuerza (Daix PMZ125-1) - Sold
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08-26-2018, 02:15 AM	#2
Chinabike Join Date: Jan 2018 Posts: 361	I think 120/70 front and 130/70 back is best i'm might get two 120/70 i don't like the fatty back tire look. and if you go any bigger on the front it might not clear your fender.
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