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Discussion Starter · #1 ·
Hello, everybody. First post here, excited to be part of the community!

Just picked up a Z125 Pro. Looking to replace the stock tires, probably with some Kenda KD1s, but I'm conflicted on sizing.

Is there an advantage in going with a 120/70 front over 100/90? Any trade-offs? I see a lot of people running that size here, but I'm not sure why. Perhaps it has to do with availability.

I understand going with a 130/70 or 120/80 rear can yield a higher top speed, but will the bike have enough power to reach it? I've read of people losing power at the top of third/into fourth gear due to tire size. I definitely don't want to suffer that type of acceleration loss.

Would stock size be best until I get used to the bike and have the experience to know what I'd like out of it, or is there a clear advantage to going with a different size?

The bike is for daily street use with spirited riding whenever I can get it in.

Any recommendations based on experience would be much appreciated!
 

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Discussion Starter · #3 ·
Thank you for the reply!

After several hours of scouring all of the tire threads, I decided to stick with the stock size until I learn the bike and figure out what I'd like to get out of it. The Kendas were cheap enough and will provide better grip until I figure that out.

Could have been wise to give the stock tires a chance, but having something stickier as a base may help point me in the right direction for future sizing.
 

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Thank you for the reply!

After several hours of scouring all of the tire threads, I decided to stick with the stock size until I learn the bike and figure out what I'd like to get out of it. The Kendas were cheap enough and will provide better grip until I figure that out.

Could have been wise to give the stock tires a chance, but having something stickier as a base may help point me in the right direction for future sizing.
In my personal opinion (though surely it's fact) is that the larger tire size increases overall stability while riding the bike, especially pegged out doing 55-60.

I no longer feel like I'll be blown off the road while doing 60 and we have a gusty/windy day, with the stock tires it got quite squirmish and I hated the way it felt. There are other factors involved that may play a role in that like height/weight but in the end, I would never go back to stock.
 

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Discussion Starter · #6 ·
In my personal opinion (though surely it's fact) is that the larger tire size increases overall stability while riding the bike, especially pegged out doing 55-60.

I no longer feel like I'll be blown off the road while doing 60 and we have a gusty/windy day, with the stock tires it got quite squirmish and I hated the way it felt. There are other factors involved that may play a role in that like height/weight but in the end, I would never go back to stock.
By larger, do you mean in width? Was really considering wider tires for more stability, as I haven't ridden in 18 years. What size are you running?
 

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I'm having some Michilin Power Pure's 120/70 up front and 140/70 in the rear installed this weekend. After reading other tire / size posts on here my understanding is the 140 rear will correct the speedo and since the Z will never be a "fast" bike it might as well look bad *** and feel more stable! Good luck whatever route you decide to go!
 

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Discussion Starter · #8 ·
I'm actually having second thoughts about ordering stock size. Think I'm going to try to change my order to 120/70 F and 130/70 R in the morning. Hopefully acceleration/top speed aren't adversely affected. The extra stability would be nice considering I haven't ridden in about 18 years.
 

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I'm actually having second thoughts about ordering stock size. Think I'm going to try to change my order to 120/70 F and 130/70 R in the morning. Hopefully acceleration/top speed aren't adversely affected. The extra stability would be nice considering I haven't ridden in about 18 years.
Those sizes seem to be a popular choice as well!
 

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. After reading other tire / size posts on here my understanding is the 140 rear will correct the speedo
True if it's the right size 140
The 140 is only the WIDTH of the tire and any tire width change dose not change the speedo
Only the HEIGHT of the tire is what effects the speedo readout and changes the gearing ratio as well
A 140/70 should correct the speedo within +/- 1mph
A 140/80 or 140/90 will throw the speedo way off

To correct the speedo closer to actual real speed a 19 1/2" tall tire is closest to correcting the speedo within +/- 1 mph

A 15 tooth counter sprocket with the stock 18 1/2" tall tire also corrects the speedo within +/- 1 mph

Font Number Parallel Document
 

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Discussion Starter · #11 ·
I ended up catching my order in time and going with the 120/70 130/70 combo.

Hoping to be able to ride soon and get some seat time on stock tires so I can get a valid comparison with the new setup.
 

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I ran a set of KD1's in stock sizes this past season after using up the rear of the stock IRC's. The reason I didn't mess with changing sizes is I didn't want to add anymore unsprung weight than necessary, I also just barely got to using the edge of the stock rear and that was only from parking lot cone carving. Even the tightest twistiest backroad at illegal speeds left at least a 1/2-3/4" of unused rear tire.

TBH I never had a problem with grip or stability of the stock tires, and in retrospect I should have hunted around for a new IRC rear as the front was barely worn and I managed to get 5k miles out of the rear.

It's not the end of the world but I'm not sure the extra grip is worth half the tire life. Not that big a deal as I bought them pre-pandemic and bought 2 rears and 1 front to take advantage of free shipping. My only nit pick with the kenda's being tire life.

Hopefully when the Kenda's are all used up I can find a set with a dual compound rear in the stock size as the center wears way faster than the edges...
 

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I have the 120/80 rear and im at the edge of that tire with nothing left at the race track... The front maybe has a quarter of an inch left on the sides. I finally tracked a set of kd2 tires and with the supposed more edged curve i should be able to lean more to use up the front or have spare in an emergency.

The kd2 only comes in one size which is 120/80 rear and stock front.
 

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[QUOTE="Azlar49, post: 139723, member: 13543"
The kd2 only comes in one size which is 120/80 rear and stock front.
[/QUOTE]

That's why I haven't tried the KD2s yet. I used to run the 120/80 rears but they are a pound heavier and the wider footprint of the 130/70 seems to grip better at the limit.
Here's what a stock IRC, 130/70 KD1 and 120/80 KD1 look like together. Quite a difference in dimensions and in feel at the track.

Tire Wheel Automotive tire Synthetic rubber Tread
 

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"...as the center wears way faster than the edges..."

Hmmm. My KD1s have the opposite problem. ;)

View attachment 27132
Man I wish there was a track near me that was the appropriate size for the z. There is actually a large multi-layout cart track a half hr. from me but they don't allow bikes at all... they don't want downed bikes and spilled fuel messing up the track so they say...

I'd love to give the z a go on track.
 

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Man I wish there was a track near me that was the appropriate size for the z. There is actually a large multi-layout cart track a half hr. from me but they don't allow bikes at all... they don't want downed bikes and spilled fuel messing up the track so they say...
Well, if there are plenty of local kart owners keeping your track busy, it might be hard to get access. I think karts can also spill fuel, so... Out here in SoCal the karts are less plentiful and most tracks see way more minimoto riders so they are happy to have us. Some even have "Bikes Only" track days. It just depends on the individual track operator.

Here's a listing from Minimoto Alliance of all the tracks that are minimoto friendly. Maybe there's one near you?

 
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