Ultra Motor Europa rear tire problem

[WhatcomRider]

Introduction

Greetings. Three weeks ago I purchased a very lightly used Ultra Motor Europa bike with a "24V / 235W" marked Heinzmann motor for $350. It came with an 11lb. 36V / 10 cell Li-ion battery but with no charger. While in storage the battery had dropped down to 22.3V with the lowest cell at 1.7V and I had no idea if it could be salvaged. I bought a Li-ion charger on ebay from Juiced Riders and carefully nursed the battery back to life with 10 or so brief charges in a row until the BMS "woke up" at 30 volts. The battery is now working within spec and remains cool as a cucumber during charging and discharging. Other than a cross-threaded crank arm (original owner error) that had to be replaced the bike has been working well for me until a few days ago...

The Problem

Two flat rear tires in a row where it appears that the base of the valve stem split - most likely caused by the tire rotating on the rim. The first time on a very steep but short descent with hard braking. The second time on a new tube with no particularly hard stress on mostly smooth pavement. Tires had been inflated to 60 +/- 5 lbs. and appeared to be seated evenly on the rims before the flats occurred. The rims are Alexa DM18 with 18mm inner rim width and 570mm outside diameter. The tires are Kenda Komfort (K 841A) 26 x 1.95 marked for HB-575 rims. The tire liners are 35mm wide and 3mm thick. The rim tape is 20mm wide. The valve stem hole in the rim has no burrs or overly sharp edges. So I am thinking that either there is a rim / tire size mismatch, the rim tape is too wide thus interfering with tire seating, or the tire liners are causing problems, or some combination thereof. Any other ? Should I replace the tires / rim tapes? I am thinking Schwalbe Marathon 26 x 2.00 tires would work well on this bike.

P.S. I am 155lbs. so rider weight is not an issue.

 

[dogman dan]

Sounds to me like a bad batch of tubes. Switch brands or at least stores for awhile. Rubber is wierd, and flaws can happen in the process, resulting in a tube that likes to tear rather than stretch. I've had it (stems tearing out) happen a few times to me over the years, but not two in a row like that.

Since you didn't underinflate, I doubt any of the liners or rim tape is squirming around enough to cause it. The heinzmann is a torquey motor, but at 60 psi you shouldn't be seeing the tire sliding down and angling the stem.

But it could be a that bad fit of the tire. Is it stupidly easy to get on the rim? Really loose could do it.

 

[Drunkskunk]

Interesting problem. The simple answer is the tire is too big if it's slipping at 60lbs.
But I wanted to back that up with numbers, so I went googling. Unfortunatly, All i found was conflicting answers, some saying the HB-575 is the same as a 559 rim crochet rim, some saying it isn't. some arguing that a HB-hooked bead is diffrent from a Crochet, some saying its the same.

In the end what matters is that if your tire can slip at 60lbs pressure, it's too big. It may well be that it's made too big, or it might just be a defect. it doesn't matter. The only cure is a new tire. I would try a diffrent brand, one known for a tight fit, like Maxxis or Schwabble.

 

[WhatcomRider]

Dogman, I don't know - two different tube brands and the tire was pretty tough to get off, I was concerned that my plastic tire levers would break. It's possible that there's a misfit which is bad because there is not much rim wall for the tire to grab on to.

 

[WhatcomRider]

Thanks DS, I'll go with your answer - new tires it will be. One LBS in town quit carrying Schwalbe tires because they were so difficult to wrestle on and off, but in some ways that is reassuring.

 

[WhatcomRider]

Follow Up

After studying a draft copy of the ISO 5775-2 spec dealing with bicycle rim sizes, I know for sure that the Kenda Kontact tires are NOT compatible with the rims on my Europa. The tires are specifically marked for HB-575 rims which are hooked bead rims for non wire-reinforced bead tires that depend on air pressure alone to hold the tire on the rim. The rolled flanges are larger in radius and the rim walls are deeper and more curved than on the far more common crochet rims (aka clinchers) which depend on wire reinforcement in addition to air pressure. Also, 575 refers to the a rim diameter which is possibly 5 to 16 mm larger that the rims I have. Apparently the HB-575 rims were used on some European bikes. Somehow the wrong tires got mounted on my Europa - they were too loose on the rims and the rear one rolled twice, each time tearing the base of the valve stem.

I decided to go Continental brand all the way - new rim tapes, tubes, and tires (Contact Eco Plus) from BikeTiresDirect in Portland OR. All of which were a pleasure to install and I am happy with the smooth ride and rolling performance of the new tires which are specially designed for e-bikes.